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A comment on LightSail 2 Spacecraft Successfully Demonstrates Flight by Light. Parent comment

Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by e12e on Thursday August 01, 2019 @11:54AM (#20584956)
I wonder if it'd be feasible to just have the sail be a one way mirror? Transparent on the "front".
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Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by doctorphil on Thursday August 01, 2019 @01:29PM (#20586172)
There are no known materials that act as a one way mirror. We don't expect to find any such material. With a one way mirror it would be easy to lower global entropy.
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Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by cben on Friday August 02, 2019 @09:55AM (#20592910)
However, one side reflective/white one absorbing black is possible. I guess the weight of extra paint is not attractive, compared to attitude control which you need anyway.

EDIT: this matters because full 180° reflection is like "bouncing" the photon to opposite velocity, can up to double exchanged momentum vs absorption. (This is why reflective mylar is nice)

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